How dinosaurs spent their lives remains a great mystery of paleontology. We know they ate a lot, and presumably they had sex somehow. But it's almost impossible to prove the existence of more complex dinosaur behaviors...until now.

Thanks to some teeth from the Jurassic period dinosaur Camarasaurus, we have the first clear evidence that dinosaurs migrated over great distances. A slightly smaller relative of plant-eating sauropods like Brachiosaurus and Apatosaurus, Camarasaurus grew up to fifty feet long and lived in what is now Wyoming and Utah.

Colorado College researcher Henry Fricke examined the oxygen isotopes levels in 32 Camarasaurus fossil teeth.The specific ratio of different isotopes can provide an exact signature of where the dinosaurs drank, and that can be compared to rock samples that date to the same time and place. He found the teeth were not an exact match for the rocks, which means Camarasaurus must have left its natural habitat on occasion.

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Teeth build up multiple layers over the life of their owner, and each layer preserves the isotopic signature of where the owner was drinking at that given time. Fricke discovered that the layers changed in Camarasaurus over a five month period, which strongly suggests the dinosaurs migrated seasonally. It's the best proof yet that some dinosaurs did indeed move around on a regular basis.

Fricke explains:

"In a theoretical sense, it's not hugely surprising. They are huge - they would probably have eaten themselves out of house and home if they stayed in one place. Now we have evidence that demonstrates that, and a method to move forward and study other dinosaurs."

Camarasaurus likely had to migrate because its regular home was a low-lying floodplain that could easily enter extreme dry periods. Since this was a fairly large population, Camarasaurus wouldn't be able to cope with any research shortages, and the fossil teeth suggest they solved this by moving to higher altitudes. This would have involved migrating at least 200 miles, and it's possible some migrations were much longer.

Now that we know one species migrated, Fricke is hopeful he can find evidence that others did as well. In particular, modern predators often follow migrating herbivores, and it stands to reason that carnivorous dinosaurs like Allosaurus would have done the same, since it would have been ridiculously easy to pick off a Camarasaurus as it was slowly moving towards it new home.